Abstract

Groups of individuals (three replicates of four treatment groups of 10 individuals) of Daphnia magna were exposed to nutritional stress in the forms of reduced food quantity and/or quality (phosphorus-limitation). Both types of stress led to reduced growth and reproduction, producing a gradient from surplus of high quality food to severe nutritional stress. There was no effect of nutritional stress on developmental instability measured either as fluctuating asymmetry or as phenotypic variability in body shape. Computer simulations confirmed that the lack of effect was not simply due to low statistical power. Low food quantity led to larger variability among individuals in overall body size, but this was most likely due to exploitative competition and competitive dominance of larger individuals. Low food quantity also led to increased occurrence of abnormal postabdominal spines (two spines appearing from one basis), but other analyses suggested that abnormal spines may actually represent an adaptive phenotypic response rather than a deviant phenotype caused by developmental instability. In conclusion, the results suggest that Daphnia magna are able to maintain high developmental stability even under extreme nutritional stress. This casts doubt on the utility of using any of the investigated measures of developmental instability as general indicators of environmental stress.